Roger A. Green

Quadrature receiver mismatch calibration

This article introduces nonlinear regression techniques to estimate gain and phase mismatches between the in-phase (I) and quadrature (Q) branches of a quadrature receiver. Under modest assumptions, the system intrinsically follows a nonlinear regression model. The algorithm is effective, easily implemented, customizable, and requires few assumptions. Large-sample, jackknife, and bootstrap techniques provide on-line error assessment and parameter inference.

An optimized multi-tone calibration signal for quadrature receiver communication systems

Communication systems are subject to stringent image rejection requirements. Thus, accurate and regular field calibration is important. Regression techniques are effective in the calibration of quadrature receiver systems. These techniques require the transmission or injection of a calibration signal to estimate potentially frequency-dependent errors. Existing regression-based methods use nonlinear models with signals that calibrate only one frequency at a time. This paper recasts the problem in terms of linear regression and develops an optimized multi-tone calibration signal for quadrature receiver communication systems. Linear regression ensures closed-form solutions that can be computed in real-time by using adaptive filtering techniques. Simulations demonstrate the advantages of the multi-tone signal: simultaneous multi-frequency calibration and minimal interference with information bearing communication channels. At the same time, the benefits of regression-based calibration are also realized: modest model assumptions, effective performance assessment, and accommodation of non-uniformly sampled or missing calibration data.

Maximum likelihood technique to quadrature parameter estimation

In array processing applications, quadrature receiver gain imbalance can significantly degrade the performance of direction-finding algorithms and adversely affect the received signal quality. These errors are present, to some degree, when quadrature receivers are used with sensor arrays, and can be partially compensated for by estimating these error parameters and correcting for them during array calibration. Of particular interest is finding the best estimator possible to ensure proper and accurate calibration. This paper derives the maximum likelihood (ML) estimator for the quadrature gain errors, based on a measured array manifold. The bias and variance of the estimators are derived and simulations are incorporated to demonstrate estimator effectiveness.<<ETX>>

Software-gated pulse-Doppler ultrasound for a DSP-based blood flowmeter

Traditional short-gate pulse-Doppler devices rely on hardware gating to measure a blood vessels velocity profile. In the same spirit as software radio, advanced digital signal processor (DSP) technologies suggest software gating as an alternative to traditional hardware gating methods. By way of computer simulation, this paper explores the viability of a software-gated pulse-Doppler technique for measuring a blood vessels velocity profile. Simulations utilize a particle model that is then mixed, filtered, and sampled. Spectral analysis provides velocity profile information. Preliminary results suggest software gating is not only feasible but, also advantageous.

Optimization of multisine excitations for receiver undersampling

An algorithm for optimizing the frequency distribution of an arbitrary multisine signal is presented to reduce the power consumption and computational complexity of a multisine receiver. By careful selection or adjustment of each frequency component in the applied multisine signal, undersampling and frequency aliasing in the receiver can be used to reduce the circuit power consumption contributed to operating frequency and also increase the bin utilization of the discrete Fourier transform (DFT) analysis frequencies. One example of an optimized 25-tone log-spaced multisine signal shows that the sampling frequency in the receiver can be reduced to only 4% of the Nyquist frequency. In addition, the computational complexity of calculating the DFT is reduced by a factor of 38.

Internal calibration techniques for quadrature receiver mismatch errors

The performance of systems requiring the use of quadrature receivers is significantly degraded in the presence of mismatch errors between the In-phase (I) and Quadrature (Q) branches. This paper discusses the mismatch problem and introduces promising solutions. These solutions are independent of communication format, which improves the generality and flexibility of the techniques.Current literature emphasizes estimation of either local oscillator (LO) mismatch or frequency dependent path mismatch using an external calibration signal. This paper develops techniques to estimate both LO mismatch and path mismatch using internally generated calibration signals derived from the system local oscillator. Once the mismatch errors are obtained, LO mismatch can be corrected by analog adjustment and path mismatches are corrected digitally.

B-spline enhanced time-spectrum analysis

A new technique for the time-spectrum analysis of non-stationary signals is presented. The proposed technique smoothly fits a systems time-varying spectral coefficients using the combined methods of Fourier analysis and B-splines. The resulting algorithm is efficient and generally effective. Algorithm assumptions and limitations are identified; performance is explored using simulated data. Provided certain conditions are met, the algorithm degenerates into the well-known cases of the simple and averaged periodograms. Methods are presented to calculate knot spacing based on the frequency and geometric properties of the ensuing time-spectrum curve. Near real-time capabilities are also discussed. Finally, the method is compared with other time-spectrum analysis techniques such as the evolutionary periodogram (EP).

Getting a handle on MATLAB graphics

Among engineers and scientists, MATLAB is one of the most popular computational packages. Part of MATLABs popularity stems from its simple, yet sophisticated, graphics capabilities. While basic plots are relatively easy to obtain, specialized plots require a little more effort to produce. This article introduces MATLABs Handle Graphics, which provides a mechanism to fully control and customize graphics objects in MATLAB. With a basic understanding of Handle Graphics, users can produce plots that meet the unique needs and quality standards commonly required by the profession, several examples are presented to illustrate the concepts.

An Introduction to Scholar Teams: A Method to Enhance DSP Education and Competence

This paper introduces the concept of scholar teams (STs), discusses strategies to successfully implement STs, overviews the results of the first two years of comprehensive ST trials conducted in the Electrical and Computer Engineering (ECE) department at North Dakota State University (NDSU), and details a specific ST, the digital signal processing (DSP) ST, to illustrate the benefits of STs, particularly from a DSP education perspective

A modified Goertzel structure for efficient real-time blood velocity profile estimation

Many applications utilize short-gate pulse-Doppler schemes to extract velocity information, such as a blood vessels velocity profile. Advances in signal processing hardware permit software gating to replace traditional hardware gating. Although software gating can be advantageous, the added computational complexity hinders real-time operation, which is clinically desirable. Thus, high-resolution, real-time operation requires efficient algorithms for data processing. This paper develops a modified Goertzel structure for efficient real-time blood velocity profile estimation. When compared with traditional computational methods, this modified structure offers significant advantages with regard to memory, number of operations, and latency of estimation. Simulations are provided to demonstrate algorithm effectiveness.